Understanding Pregnancy Due Date Calculation

Calculating your pregnancy due date is an important first step in your prenatal journey. Our due date calculator uses established medical guidelines to estimate when your baby might arrive.

How Due Dates Are Calculated

The most common method for calculating due dates is based on the first day of your last menstrual period (LMP). This method adds 280 days (40 weeks) to your LMP date. This timeline includes the two weeks before conception actually occurred, which is why pregnancy is typically counted as 40 weeks rather than 38.

Last Menstrual Period (LMP) Method

Using the LMP is the standard method for calculating due dates. Healthcare providers use this method because most people know when their last period started, but few know exactly when they ovulated or conceived.

Conception Date Method

If you know your conception date, you can calculate your due date by adding 266 days (38 weeks). This method is less common because it's difficult to know the exact date of conception unless you were tracking ovulation very carefully.

IVF Transfer Date Method

For pregnancies achieved through in vitro fertilization, the due date calculation is based on the embryo transfer date and the age of the embryo at transfer. This provides a very accurate due date since the timing is precisely known.

Accuracy of Due Date Calculations

It's important to remember that only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated due date. Your healthcare provider may adjust your due date based on ultrasound measurements, especially if they differ significantly from the LMP calculation.

Trimesters of Pregnancy

Pregnancy is divided into three trimesters:

• First trimester: Weeks 1-13 - This is when most early development occurs and pregnancy symptoms often begin.
• Second trimester: Weeks 14-27 - Often called the "honeymoon period" as many early symptoms subside.
• Third trimester: Weeks 28-40 - The final stage of pregnancy as you prepare for delivery.

Important Pregnancy Milestones

Throughout pregnancy, there are several key milestones:

• First ultrasound: Typically between 8-14 weeks
• Detectable heartbeat: Can often be seen on ultrasound around 6 weeks
• Viability: Around 24 weeks, when a baby has a chance of survival outside the womb
• Full term: 37 weeks, when baby is considered developed enough for delivery